Songbird Numbers May Indicate Trouble in Northwest Forests

Purple finches, indicators of healthy coniferous habitat, are declining in the Northwest, according to data from the Klamath Bird Observatory. (Photo by J. Livaudais)

(CN) – Numerous North American songbird populations are declining, and conservationists are not sure why – although 10 years of data indicate the reasons may be as varied as the birds themselves.

Theories about why these bird populations are declining include reproductive issues and poor survival rates of adults, as well as possible changes in environmental conditions.

In an effort to shed light on this murky problem, researchers analyzed 10 years of data from banding stations – where birds congregate in large numbers during migration – in the Pacific Northwest, which they detail in a study published Wednesday in the journal The Condor: Ornithological Applications.

“Before we can understand the impact of threats to bird populations, we first need to understand what’s happening where,” said co-author John Alexander, executive director of the Klamath Bird Observatory, which led the research.

The team’s findings reveal that the issues plaguing songbird populations vary by group and location.

The 12 songbirds the researchers studied were chosen based on either regional conservation concern or habitat quality. The team used data collected between 2002 and 2013.

Three of the species – the yellow-rumped warbler, the dark-eyed junco and the purple finch – were declining, which the team attributes to habitat-quality issues. However, numbers of the yellow-breasted chat and the black-headed grosbeak increased, though trends varied by site.

The researchers also found that breeding issues have contributed to the decline of three other songbird species. However, adult abundance reflected the previous year’s productivity for only one species, the yellow warbler, which suggests that local spawning is not the main force behind such population declines, according to the report.

“This study presents trends from regional-scale monitoring and just begins to scratch the surface of understanding population dynamics, variation in demographic rates, and drivers of population change across our landscape, which is vital information for developing effective conservation plans,” Alexander said.

“It also highlights concerns about forest-associated species in this region – the need to balance timber harvest, a mixed-severity fire regime, and endangered-species management continue to present complex conservation challenges.”

The team encourages further research in order to identify additional population-level and environmental dynamics that could be fostering songbird species declines.

“This work is so important,” Rockwell said. “We need robust baseline data if we are going to be aware of any kind of population change, let alone be able to do something about it.”